Measuring and circumventing Internet censorship

Abstract: An ever increasing amount of governments, organisations, and companies employ Internet censorship in order to filter the free flow of information.  These efforts are supported by an equally increasing number of companies focusing on the development of filtering equipment.Only what these entities consider right can pass the filters. This practice constitutes a violation of the Universal Declaration of Human Rights and hampers progress.  This thesis contributes novel techniques to measure and to circumvent Internet censorship. In particular, we 1) analyse how the Great Firewall of China is blocking the Tor network by using active probing techniques as well as side channel measurements, we2) propose a concept to involve users in the process of censorship analysis, we 3) discuss the aptitude of a globally-deployed network measurement platform for censorship analysis, and we 4) propose a novel circumvention protocol. We attach particular importance to practicality and usability. Most of the techniques proposed in this thesis were implemented and some of them are deployed and used on a daily basis.  We demonstrate that the measurement techniques proposed in this thesis are practical and useful by applying them in order to shed light on previously undocumented cases of Internet censorship. We employed our techniques in three countries and were able to expose previously unknown censorship techniques and cooperation between a corporation and a government for the sake of censorship. We also implemented a circumvention protocol which was subsequently deployed and is used to evade the Great Firewall of China.